A multiple access system uses a beamforming (BF) technique using multiple antennas for improvement in performance of the system and an increase in capacity. Generally, beamforming represents that a plurality of antennas areis disposed at predetermined intervals, and weighting vectors given for each antenna for the same signal are multiplied and transmitted.
In order to obtain an optimum weighting vector for each antenna, a zero forcing (ZF) algorithm can be used. The zero forcing algorithm, which removes an interference signal by previously multiplying a transmitting signal by an inverse matrix of a channel at the time of transmission, performs beamforming so as to not generate interference in another transmitter rather than concentrating power on an object receiving information, such that it is regarded as an unselfish algorithm.
To the contrary, a maximal ratio transmission (MRT) algorithm performs beamforming in order for power to be concentrated only in the direction of a specific transmitter, not considering interference affecting another receiver, such that it is regarded as selfish algorithm.
Therefore, in the communication environment having a good channel condition, high transmission efficiency can be expected when the selfish algorithm such as the maximal ratio transmission beamforming is used, and in the communication environment having a bad channel condition, high transmission efficiency can be expected when the unselfish algorithm such as the zero forcing beamforming is used.
However, since the channel condition is variable according to time, there is a demand for properly coupling and applying the selfish algorithm and the unselfish algorithm according to the channel condition for obtaining optimum transmission efficiency.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.